The invention relates to a device for storing and unwinding rolls of material in bookbinding machines.
In many production processes in the manufacture of bookbinding products, materials in web form are processed which, unwound endlessly from a roll, are fed to the production process either in a timed manner or continuously, and are cut off to the required length at the moment of joining or immediately before it. For the continuous processing of such rolls of material, roll-changing devices are known which connect the end of a web of material unwound from one roll of material to the beginning of a web of material of the same kind which is to be unwound from another roll of material.
By way of an example, DE 36 14 221 describes such a roll-changing device for webs of screening material, in which the two webs of material are connected to one another with the aid of an adhesive tape which overlaps the join between the ends of the webs. Before the roll-changing operation, the beginning of the web of material to be unwound from a roll of material is clamped-in in a gripping device above the path of movement of the web of material drawn off, cut off in a straight manner at a cutting edge which defines the line of the join, and provided with an adhesive tape which protrudes at the beginning of the web of material. At the moment the roll-changing operation occurs, the gripping device travels downwards, with the web of material which is to be unwound and which is held in a clamped-in manner, into the plane of the unwound web of material, at the same time severs the unwound web of material in a straight manner against a supporting table with the aid of the cutting edge, and immediately afterwards touches down, with the protruding adhesive tape, on the end of the unwound web of material. After the adhesive tape has been firmly pressed on, the gripping device releases the web of material to be unwound, elements on the said gripping device below the path of movement of the web of material are pivoted out sideways, and the gripping device travels back upwards into the starting position.
The rolls of material are located on roll-mountings which hold the core of the roll, in order to permit low-resistance unwinding of the web of material by a system of drawing-off rollers. Under these circumstances, the end faces of, in particular, narrow rolls of material are supported by metal side plates. In the event of interruptions in the drawing-off of the web of material, the rolls of material have to be braked so that they do not continue to unwind automatically because of rotational energy. To that end, the metal side plates are pressed against the end faces of the surfaces of the material by the application of a pneumatically generated force at the moment of braking, or of a constantly applied spring force. What is common to both solutions is that the braking force is constant and is not proportional to the mass moment of inertia to be braked. That is to say, a roll of material with a large outer diameter and thereby a large mass moment of inertia is, under certain circumstances, braked in too weak a manner, whereas a small roll of material is braked in too strong a manner. In the case of braking with constantly applied spring force, unnecessarily high drawing-off forces are generated and it proves difficult to reconcile low-resistance unwinding with safe braking.
In addition, in the case of unrolling devices with integrated roll-changing devices, at least two roll-mountings are necessary, which have to be brought into position in an alternating manner for the unwinding of a roll of material by a drawing-off system, or for the manual exchanging of an unwound, empty roll of material for a full one. As a result of this, the device becomes expensive.
The object of the invention is to propose a device for storing and unrolling materials in web form in bookbinding machines equipped with roll-changing devices, with the aid of which device functionally reliable unwinding and changing of the rolls of material can be achieved in a manner which is simple and thereby economical and easy to operate. This object is achieved in a surprisingly simple and economical manner by means of a device having the features of the subject invention.
Because of the upright accommodation of rolls of material in a shaft having side walls for supporting and guiding the said rolls of material and having movable supporting elements for supporting, in a rolling manner, the unwinding roll of material by its superficies, and also having a stationary, almost horizontal floor for storing, until the rolls are changed, the roll of material to be unwound, the expensive roll-mountings of a roll-changing device, which are otherwise present in multiple form, are dispensed with. When the web of material is drawn off, the unwinding roll of material unrolls on the supporting elements by its superficies, as a result of which almost identical unrolling conditions prevail with different diameters of the rolls of materials. Since the unwinding roll of material is supported against one or more supporting rollers at the end face of the shaft in the direction of drawing-off of the web of material, the roll of material migrates, in the course of time, into a corner of the unwinding region and frees the unwinding position, when roll changing occurs, for a subsequent roll of material which, with the drawing-off of the web of material for the first time, unrolls horizontally on the floor of the shaft in the direction of the drawing-off device, and thereby moves into the unwinding position automatically. The storage place is thereby free again for a new roll of material.
As a result of advantageous further developments in the region of the unwinding position, the unwinding roll of material is braked when the offtake for the web of material is stopped, so that the said roll of material continues to unwind only to an immaterial extent, and rolls back into a depression, as a result of which any web of material which has unwound to too great an extent is wound on again. When the offtake for a web of material is started up, the roll of material is set in motion with relatively low drawing-off forces, and first of all unrolls on the supporting elements and moves up onto one or more supporting rollers. As a result of the resilient application of the said supporting rollers, preferably by means of a carrying arm holding the supporting rollers, the translatory movement of the roll of material is gradually converted into a movement of the supporting elements, without peaks in the drawing-off force which tear the web of material apart occurring in the process.